In completing and producing oil wells, one can often foresee that a lower part of a tool string must subsequently be disconnected from the string and left downhole in the borehole. This is especially so in well completion work, wherein the lower tubing string is sometimes severed by use of clever explosive devices and dropped to the bottom of the hole. An important example of the desirability of separating a tool or pipe string is found in U.S. Pat. No. 3,706,344 to which reference is made for further background of this invention.
Accordingly, it is desirable to be able to separate a tool string at any predetermined location along its length. It is further desirable that the separation of the string be achieved while avoiding explosives because of the inherent dangers associated with the use of explosive devices, especially when used downhole in boreholes. Moreover, it is especially desirable that the separation of the string be effected by a wireline operation, and that it be brought about in an inexpensive and foolproof manner.